Glossary 623 



E 



Ear: The organ of hearing. 



Earth : The planet on which we live ; soil. 



Echo: Repetition of a sound due to reflection of sound waves. 



Eclipse: The darkening of a luminous heavenly body, such as the sun, 

 by another heavenly body passing between it and the eye ; the darken- 

 ing of a luminous heavenly body by another heavenly body coming 

 between it and its source of light, as the darkening of the moon by 

 the earth. 



Efficiency: Ability to accomplish work with a minimum of effort. 



Effort: Exertion of force or power to overcome resistance. 



Electrical resistance: The opposition offered by a conductor, such as 

 a wire, to the passage of an electric current through it, causing heat. 



Electric cell: A device for producing a current of electricity. 



Electricity: A form of energy which, under the proper conditions, will 

 flow and exert pressure. It is divided into static, or stationary, elec- 

 tricity and current, or flowing, electricity. Both static and current 

 electricity are divided into two types, positive electricity and negative 

 electricity. 



Electric motor: A machine for changing electrical energy to the energy 

 of motion. 



Electrification (e-lek-tri-fi-ka'shwn) : State of being charged with elec- 

 tricity. 



Electrodes (e-lek'trodz) : The plates in an electrolysis apparatus or in 

 an electric cell, to which the wires are attached. 



Electrolysis (e-lek-trol'i-sis) : The breaking up of a substance into its 

 elements by means of electricity, as the decomposition of water into 

 hydrogen and oxygen by electricity. 



Electromagnet (e-lek-tro-mag'net) : A piece of soft iron magnetized by 

 the passage of an electric current through an insulated wire wound 

 around it. 



Electromotive force (e-lek-tro-mo'tiv) : Electrical pressure in a con- 

 ductor. 



Electron (e-lek'tron) : A minute particle of negative electricity. 



Electron theory: A theory of electricity which assumes that all atoms 

 are made up of minute particles of positive and negative electricity. 

 The positive particles, called protons, form the center of the atom, 

 around which revolve Jthe negative particles, called electrons. 



Electroplating (e-lek'tro-plat-ing) : The process of coating a cheaper 

 metal with silver, gold, or some other metal by means of electricity. 



Electroscope (e-lek'tro-skop) : An instrument used to determine the 

 presence of electricity. 



Electrotyping (e-lek'tro-tip-ing) : An electric process of making plates 

 from type for use in printing. 



Element: A substance which cannot be broken up into other kinds of 

 matter. (For important elements see page 28.) 



Ellipse: ^An oval-shaped curve having greater length than width. 



Elodea (e-16'de-d) : A water plant whose cells are much used for ob- 

 serving the circulation of protoplasm. 



Embryo (em'bri-6) : A young plant in the early stages of development. 



Emergency: An unexpected occurrence calling for quick action. 



Emetic (e-met'Ik) : A substance which will cause vomiting. 



Emulsion (e-mul'shwn) : A mixture of two liquids which do not unite 

 with each other to form a true solution, as soapy water and grease. 



